Hello all.
I have an issue with the AC on a 1999 Grand Caravan. It has front and rear AC.

History.....
I had to replace the front expansion valve.
I evacuated the system, replaced the valve, vacuumed to -30psi, held for 20 minutes to -28psi.
Added 24oz of refrigerant and the system checked at 35psi low side, 210psi high side. Ac was blowing cold. I found this a bit bizarre because the spec for front/rear on this vehicle is 46oz.
After a few hours, I go back and it's not blowing very cold. I put the gauges back on and the numbers are the same. 35 low, 210 high. If I let it run for a while it will start to get cool, but not cold.
I added another 12oz, and the pressure shot to 55 low, 260 high with no change in the cooling. Now I'm at 36oz. 10oz below spec and way over on the pressure.
At first you would think that I didn't pull a vacuum before charging, and that it has more air than refrigerant. But I did.
I know the high side switch is working because when I first turn on the AC the high side will go to about 300psi before the fans kick on and the pressure stabilizes.

So my questions are....
Why is is it not taking the 46oz?
Could the rear expansion valve be causing this?
Why does it blow cold when I first put the refrigerant in, but not a few hours later, but yet have the same psi readings?
Am I missing something??

Any help would be appreciated.

 

what was the ambient temperature when you measured the pressures? If its 110* out, the pressures will be high.

"CAN" charging isn't accurate. and with high low side pressure its probably higher than can pressure.

high pressures can also be due to the system not able to release its trapped heat out thru the condenser...due to poor airflow through the condenser...bent or pinched lines at the condenser, fan shrouds not in place. if you garden hose the condenser...does everything return to normal.

If you rev the engine up to 2500rpm and hold it there...does the cold air return?